An Organocatalytic Newer Synthetic Strategy Toward the Access of Polyfunctionalized 4H-Pyrans via Multicomponent Reactions

Engaging Isatins in Multicomponent Reactions (MCRs) – Easy Access to Structural Diversity

“…used inexpensive quinolinic acid to afford spirooxindole derivatives (7 examples) in very good to excellent yields and short reaction times (Scheme 59A) [118] . 2‐Aminopyridine (2‐AP) also exhibited good catalytic activity in this 3‐MCR, although the reaction scope reported by Lalitha and co‐workers was limited (only 2 examples reported) (Scheme 59B) [119] . The same research group prepared one spirooxindole applying sodium azide as catalyst (the scope of the reaction was directed to aldehydes, rather than isatins) (Scheme 59C) [120] .…”

“…L ‐proline and melamine [63] cinchona alkaloid‐thiourea [64] cinchona alkaloids [65] THAM [93] quinolinic acid [118] 2‐aminopyridine [119] NaN 3 [120] sodium formate [121] CSA [130] BINOL‐derivative phosphoric acid [153] …”

Organocatalyzed Three-Component Synthesis of Isoxazol-5(4H)-ones under Aqueous Conditions

“…For these reasons, the implementation of synthetically useful chemical reactions in the aquatic medium has attracted the attention of many chemists from the point of view of green chemistry as well as economically. 11 Recently, 2-aminopyridine (2-AP) has been used as commercial availability, low cost, environmental friendliness, and reusability organocatalyst for the synthesis of various heterocyclic molecules, including tetrahydro-4H-chromenes, 12 polyfunctionalized 4H-pyrans, 13 1H-pyrazolo [1,2-b]phthalazine-2-carboxamide, 1H-pyrazolo [1,2-b]phthalazine, 4H-pyrano [2,3-c]pyrazole, and 4H-benzo[g]chromenes. 14 In this work, the catalytic effect of 2-AP toward synthesis of isoxazol-5(4H)-ones (4a-s) has been explored via a three-component cyclocondensation of aryl/heteroaryl aldehydes (1a-j), hydroxylamine hydrochloride (2) and β-ketoesters (3a-b) (Scheme 1).…”

“…The protons of the phenyl ring were located at δ 7.12 and 8.51 ppm as two clear and separate doublet peaks due to the para pattern. The 1 H decoupled 13 C NMR spectrum of 4c displayed five signals readily recognized as arising from two methyl (δ = 11.7 and 14.9), a CH2O (δ = 64.4 ppm), a C=Oisoxazol group (δ = 169.1 ppm), and a imine of isoxazol ring (δ = 164.1) as well as five distinct resonances at δ 115.4, 126. 1, 137.4, 151.6, and 162.7 ppm in agreement with the proposed structure.…”

Improved One-Pot, Four-Component Strategy to Access ­Functionalized Dihydropyridines by Using 4-(N,N-Dimethylamino)pyridine as a Catalyst

“…[12][13][14][15] 4-(N,N-Dimethylamino)pyridine (DMAP) can promote a number of organic transformations as a reusable catalyst, [16][17][18] and the combination of an MCR approach with organocatalysis has proved to be a most effective strategy. 19 In a continuation of our current work devoted to the synthesis of medicinally important heterocycles by using green solvents or catalysts, [20][21][22][23][24][25][26][27][28][29][30] R. Ramesh et al…”